1. Field of the Invention
The present invention relates to a chassis structure for vehicles, and more particularly to a structure in which a cross member is attached to side members that provide part of a chassis.
2. Description of the Related Art
In vehicles, there is a demand for effective reduction of an impact exerted thereon when a collision occurs. To absorb an impact exerted on a vehicle from the front, for example, the front portions of side members, which are included in the chassis of the vehicle and extend in the longitudinal direction of the vehicle, are designed to easily buckle upon receiving the impact. This buckling portion is called a crushable zone.
Further, a structure is known in which a cross member, which is included in the chassis and to which a steering device, for example, is attached, is extended between the side members. Jpn. Pat. Appln. KOKAI Publication No. 2000-229581 (FIG. 2) discloses a structure in which a cross member is fixed to side members by bolts inserted through holes formed in the bottom of side members and the corresponding upper portions of a cross member. In this case, the bolts are inserted through the holes from above the side members and secured to the side members, and then nuts are attached from below the cross member. Further, Pat. Appln. KOKAI Publication No. 10-129522 (FIG. 2) discloses a structure in which brackets are provided on side members, and a cross member is secured to the side members via the brackets. In this case, bolts are inserted from above the brackets, and nuts are attached from below the cross member.
In front-engine front-wheel-drive (FF) or front-engine rear-wheel-drive (FR) vehicles, the engine is located before the cross member within the crushable zone formed by the side members. In this structure, if an impact is exerted on a vehicle from the front upon head-on collision, the portions of the side members located before the engine buckle firstly. When the buckling motion of the side members advances up to the front end of the engine, the impact is transmitted to the engine. Since the engine is rigid, it is moved backward without being crushed. When the buckling motion of the side member further advances, the rear end of the engine collides with the cross member. As a result, the buckling motion of the side members is suppressed. Thus, the cross member interrupts the buckling of the side members, which means that the crushable zone of the size members is not sufficiently utilized.